Dehydrocyclization of hydrocarbons

ABSTRACT

PROCESS OF DEHYDROCYCLIZING C6-C10 HYDROCARBONS HAVING AT LEAST A C6 BACKBONE USING A LI,NA OR K ZEOLITE X OR Y OR FAUJASITE IMPREGNATED WITH 0.3 TO 1.4 PERCENT PT AT FROM 500 TO 560*C. AND PREFERABLY 510 TO 550*C. USING A PARTIAL PRESSURE OF H2 OF FROM 10 TO 300 P.S.I. AND PREFERABLY 50 TO 200 P.S.I. TO FORM BENZENE AND ALKYLBENZENES. OPTIONALLY THE CATALYST CAN BE TREATED WITH CHLORINE SO THAT IT CONTAINS FROM 0.3 TO 1.5 WEIGHT PERCENT CHLORINE WHICH IMPROVES THE EFFECTIVESS OF THE CATALYST.

United States Patent O1 dice 3,755,486 Patented Aug. 28, 1973 3,755,486 DEHYDROCYCLIZATION F HYDROCARBONS Masayoshi Oishi, Boothwyn, and Walter A. Butte, In,

West Chester, Pa., assignors to Sun Research and Development Co., Philadelphia, Pa. No Drawing. Filed Aug. 26, 1971, Ser. No. 175,405 Int. Cl. C07c /26, 5/27 US. Cl. 260-6735 9 Claims ABSTRACT OF THE DISCLOSURE Process of dehydrocyclizing C -C hydrocarbons having at least a C backbone using a Li, Na or K zeolite X or Y or faujasite impregnated with 0.3 to 1.4 percent Pt at from 500 to 560 C. and preferably 510 to 555 C. using a partial pressure of H of from to 300 p.s.i. and preferably 50 to 200 p.s.i. to form benzene and alkylbenzenes. Optionally the catalyst can be treated with chlorine so that it contains from 0.3 to 1.5 weight percent chlorine which improves the effectiveness of the catalyst.

BACKGROUND OF THE INVENTION In the processing of petroleum into gasoline it is known to remove the normal paraflins from the gasoline due to their very low octane ratings. This operation is conveniently carried out with a molecular sieve adsorbent. The normal hydrocarbons thus removed are then processed into more valuable products. One of these processes is reforming the normal paraflins into higher octane gasoline components. In reforming the normal parafiins are isomerized into isoparafiins, dehydrocyclized into aromatics and cracked into lower molecular weight paraflins and olefins. The process of the present invention is directed to maximizing the dehydrocycliz'ing of the normal paraflins into aromatics.

SUMMARY OF THE INVENTION The present invention relates to the dehydrocyclization of paraflins containing from 6 to 10 carbon atoms to form aromatic compounds.

The catalyst used in the present invention is a platinum impregnated zeolite. The zeolite is selected from the class consisting of zeolite X, zeolite Y and faujasite. These zeolites are quite similar in that all have cubic cells of 24.67 to 24.95 angstroms, a density of 1.29 to 1.31 g./ cm. a void volume of 0.35 to 0.36 cm. /g., and an aperture size of 8 angstroms. Faujasite has the typical composition:

( a. g)3o[( 2)so( 2)1s2] 2 Zeolite X has the typical formula:

as[( 2)se( 2)1os] 264H2O Zeolite Y has the typical formula:

sal: 2)ss( 2)136] 264H2O A further description of these zeolites may be found in Crystalline Molecular Sieves by D. W. Breck, J. of Chem. Ed., 41, 678-689 (1964). For use in the present invention the exchangeable metal ions portion of the zeolite should be lithium, sodium or potassium. Thus in the case of zeolites X or Y either lithium or potassium can be substituted for part or all of the sodium in the normal synthetic zeolite. In the case of faujasite, which is a naturally occurring zeolite, any one of lithium, sodium or potassium should be substituted for substantially all of the calcium and magnesium. Additionally lithium or potassium can be substituted for part or all of the sodium in the faujasite. These substitutions are well known in the art and generally involve treating the zeolite with an aqueous solution of a salt of the metal which it is desired to substitute onto the zeolite.

After the desired zeolite is obtained it is impregnated with from 0.3 to 1.2 percent platinum. Below about 0.3 percent platinum the catalyst is not sufficiently active. Above about 1.2 percent platinum insuflicient improvement in catalyst activity is obtained to warrant more use of expensive platinum. The zeolite is readily impregnated with platinum and chlorine by treatment with aqueous chloroplatinic acid at a moderately elevated temperature. In a typical preparation a large quantity of sodium zeolite Y such as Linde SK-40 is air dried in an oven overnight at 120 C. A g. sample of the dried zeolite is placed in a 500 ml. Erlenmeyer flask along with 200 m1. of water. The flask containing this slurry is placed in a 60 C. constant temperature bath and fitted with a reflux condenser. To the flask is added 17.25 g. of 10% chloroplatinic acid. The mixture is stirred overnight. The condenser is removed and the slurry is condensed until the remaining volume is approximately 200 ml. The slurry is then transferred to a 400 ml. beaker and placed on a hot plate while stirring at a low temperature. When the slurry can no longer be stirred it is transferred to an evaporating dish and dried in air. After air drying the catalyst is further dried with a heat lamp. The catalyst is dried overnight in an oven at C., removed, hand-ground and redried. The desired amount of catalyst is packed in the reactor being used and calcined at 500 C. in air for two hours, followed by reduction with hydrogen at 500 C. for two hours. The catalyst is then ready for use. This catalyst contains 0.56 weight percent Pt and 0.66 'weight percent C1. The amount of Pt and Cl on the catalyst is determined by the amount of chloroplatinic acid used. It is preferred that the catalyst contain from 0.3 to 1.5 weight percent chlorine.

The catalyst is then placed in a reactor and the hydrocarbon to be dehydrocyclized is passed through at a liquid hourly space velocity of from 0.1 to 40 and preferably from 2 to 15. The dehydocyclization is carried out at from 500 to 560 C. and preferably from 510 to 550 C. Above 555 C. and especially above 560 C. the amount of cracking taking place starts to increase rapidly. Below 500 C. the amount of conversion of the paraffin is too low. The amount of cyclization as opposed to the amount of isomerization increases considerably at around 510 C.

The dehydrocyclization is carried out under moderate pressure expressed herein in terms of the partial pressure of hydrogen in the reactor. The partial pressure of hydrogen generally is from 10 to 300 p.s.i. with from 50 to 200 p.s.i. being the preferred range. Below 50 p.s.i. and especially below 10 p.s.i. coking of the catalyst becomes too rapid to be economical. As the pressure increases above 200 p.s.i. and especially above 300 p.s.i. the cracking and isomerization reactions become favored instead of the dehydocyclization reaction.

Suitable parafiinic Starting materials contain from 6 to 10 carbon atoms. Any paraflin containing from 6 to 10 carbon atoms is suitable. Generally the normal paraffins are preferred because due to their low octane numbers they can be improved more than the branched paraffins which have higher octane numbers. Generally this is not a problem since ordinarily the feed stream will be the normal hydrocarbons removed by the denormalization of a Cs-Cm petroleum stream which would consist essentially of C -C normal hydrocarbons.

DESCRIPTION In Examples I and XII a pulse microreactor is used. This reactor is a stainless steel tube about 200 mm. long and having an inside diameter of 4 mm. The inside of the tube contains pyrex wool retainers which keep the catalyst in place. In each of Examples I to XII the tube is packed with 0.125 g. of catalyst. The tube is fitted in a brass mounting sleeve which contains a thermocouple in a well. The brass sleeve is in turn mounted in a 4 inch electric furnace operated on 115 volts and controlled by a 7.5 amp powerstat. The top of the tube is fitted with a silicone rubber septum mounted in a septum holder and with a carrier gas inlet. The carrier gas is deoxygenated dry hydrogen passed through the system at a rate of about 50 cc. per minute under the pressure indicated in the particular example being reported. The catalyst is preconditioned by injecting a 30 microliter pulse of the n-heptane which is being dehydrocyclized. The reactor eflluent from this injection is not analyzed. A 2 microliter charge of the material being dehydrocyclized is then injected through the septum into the reactor and the resultant efiiuent is programmed through a previously calibrated gas chromatograph. The definitions of selectivity reported in Table I are:

aromatics (wt. percent) conversion (wt. percent) X 100 Cyclization:

total isomers of same number of carbon atom (Wt. percent) conversion (wt. percent) X100 Isomerization total of lesser number of carbon atoms (wt. percent) conversion (wt. percent) X 100 Cracking containing from 7 to 10 carbons. The operating hours are the number of hours the catalyst has been on stream before the product sample was taken for the analysis reported. In Table II WHSV stands for the flow rate defined as unit weight of sample per hour per unit weight of catalyst and H/HC stands for the mole ratio of hydrogen gas to hydrocarbon feed.

TABLE IL-DEHYDROGYCLIZATION or MIXED C7-C1o NORMAL HYDROOARBONS Example XIII XIV XV Catalyst (Z) Temp., e o 510 520 520 Pressure, p.s.i- 200 200 200 WHSV 2.12 2.03 2.04 H/HC 5.13/1 5.23/1 5.17 1 Operating hours 16 7% 7% Composition, wt. percent:

Below Ga 48. 9 43. 1 40.6 6.9 7.1 2.9 2.2 17.5 19.1 as 13.6 as 7.2 85.6 90.6

1 1.30% Pt/NaX. 7 0.54% Pt/NaY. 3 1.12% Pt/NaX.

Table II illustrates that a mixed hydrocarbon stream can be continuously dehydrocyclized using the present invention.

The invention claimed is:

1. A process of reforming a feed stream consisting essentially of normal parafiins containing from six to ten carbon atoms comprising contacting said feed stream with a zeolite selected from the class consisting of zeolite X, zeolite Y and fauiasite, the metal ions of which zeolite are selected from the class consisting essentially of lithium, sodium and potassium, and which zeolite is impregnated with from 0.3 to 1.2 weight percent platinum, at from 500 to 560 (3., at a liquid hourly space velocity of from 2 to 15, under a partial hydrogen pressure of from to 200 p.s.i., whereby at least a portion of said normal paraflins are dehydrocyclized.

2. The process of claim 1 wherein the temperature is from 510 to 555 C.

3. The process of claim 2 wherein the exchangeable metal ions in the zeolite are sodium.

4. The process of claim 3 wherein the zeolite is zeo- X impregnated with the reported weight percent platinum. 0 lite Y.

TABLE I.DEHYDROCYOLIZATION OF n-HEPTANE Selectivity H3 Conver- Temp., pressure, sion, Cycliza- Isomeriza- Example Catalyst C. p.s.i. percent tion tion Cracking I 0.34% Pt/NaY 500 100 51. 2 20.1 53. 9 26.6 IL--- 0 34% Pt/NaY 500 50 62. 2 29.7 51. I 22.5 I 0 34% Pt/NaY 531 50 90. 9 55. 8 12. 9 29. l. 34% Pt/NaY 550 50 96. 8 67.3 4. 9 25.6 0 56% Pt/NaY 500 50 61. 0 40. 0 29.4 31.0 56% Pt/NaY 529 50 77. 7 48.0 15.7 33.5 0 56 Pt/NaY 549 50 92.0 51. 1 8. 3 27. 8 0 31% Pt/NaY 1 500 50 62. 7 29. 3 50.7 20. 1 0 31% Pt/NaY l 531 100 88. 8 43.9 20.2 35.9 0 31% Pt/NaY 1 531 50 80.9 56. 9 13. 2 29. 9 0.31% Pt/NaY l 550 100 95. 3 53.0 8.3 38.7 XII 0.31% Pt/NaY 550 50 97. 9 69. 0 5. 0 26. 0

5. The process of claim 3 wherein the zeolite is zeolite X.

6. The process of claim 4 wherein the zeolite contains from 0.3 to 1.5 percent chlorine.

7. The process of claim 2 wherein the exchangeable metal ions in the zeolite are lithium.

8. The process of claim 7 wherein the zeolite is zeomaining 2% a mixture of other saturated hydrocarbons lite Y.

9. The process of claim 7 wherein the zeolite is zeo- 3,369,997 2/1968 Hayes et a1. 208139 lite X. 3,301,917 1/1967 Wise 260683.65

References Cited D BERT E GANTZ P E UNITED STATES PATENTS J M NELSCQN A g Xammer 3,247,099 4/1966 Oleck et a1. 2os -13s 5 2,971,903 2/1961 Kimberlin et a1. 208119 s CL 2,971,904 2/1961 Gladrow et a1. 208-135 208-439 

